Photolithography is generally employed if a precise pattern wiring or a fine pattern thin film used in a display application and the like needs to be formed with high accuracy on substrates such as a semiconductor substrate typified by a silicon (Si) substrate, a glass substrate typified by an alkali glass substrate and a non-alkali glass substrate, a glass-epoxy substrate used as a print wiring substrate, a flexible substrate, and a plastic substrate widely used in a display application and the like.
In common photolithography, a resist material having photosensitivity (photoresist material) is first applied over the entire surface of the substrate and thermally treated to form a resist film. Then, the resist film is exposed using an exposure device such as a step type projection exposure device (stepper) and a photomask having a specific pattern. Then, development is performed using a developer containing an organic alkali and the like, and thereby a resist pattern film is formed on the substrate. Then, using this resist pattern film as a mask, the substrate is exposed to etching atmosphere by a wet-etching method or a dry-etching method. As a result, the thin film on the substrate is processed to have a specific pattern. The resist pattern film is removed by a remover containing an organic solvent and the like at an appropriate stage.
In such photolithography, it is advantageous for the production that the number of times the resist pattern is prepared is reduced as much as possible. Attempts to reduce the number of times the resist pattern film is prepared by optimizing a structure of a desired device, wiring, and the like, have been made so far, and attempts employing an exposure method also have been made.
For preparation of a TFT (Thin Film Transistor) array substrate used in a liquid crystal display device and the like, a method of locally thinning a resist pattern film using a photomask having a slit pattern (halftone exposure method) was proposed (for example, refer to Nonpatent Document 1). In this case, the resist pattern film is formed and then a first etching treatment is provided for the substrate. Then, the resist pattern film at a halftone exposure part is removed, and a second etching treatment is further performed. If the thin film on the substrate is subjected to the two-step process in such a manner, the number of photolithography processes which is generally twice can be reduced to one, although the pattern is restricted, in comparison to the case where the photolithography process is simply performed twice. Such a halftone exposure method is employed to form a TFT channel in Nonpatent Document 1.
A method using such a halftone exposure method and a reflow method in combination was also disclosed (for example, refer to Patent Document 1). This is a method in which a resist pattern is left to have an island shape near a source electrode and a drain electrode, and then deformed using organic solvent steam, thereby forming a semiconductor having an island shape.
It has been recently proposed that an ink-jet technology which has been developed in a printer application is used for preparation of circuit substrates. This is a technology of forming a metal film having a pattern and the like directly on a substrate by an ink-jet method. It has been proposed that this technology is used for preparation of wirings or passive elements (condenser, resistance, inductor, and the like). In this technology, a droplet containing metal fine particles for preparation of wirings or a droplet containing a metal oxide material and the like for preparation of condensers and the like, is added dropwise with an ink-jet device, and thereby wirings and/or passive elements are formed at a specific position on a substrate (for example, refer to Nonpatent Document 2).
A technology of forming an insulating layer or a passivation insulating layer in a TFT (thin film transistor) by applying a fluid material and performing heat treatment was disclosed (for example, refer to Patent Document 2).
In the ink-jet method, a method of providing a substrate with a pretreatment in advance before addition of a droplet also has been proposed. Such a method is aimed to reduce position accuracy when an added droplet is landed on the substrate (landing accuracy) or to improve the process speed by reducing the number of needed droplets. In this technology, a region showing lyophilicity for a material for forming a wiring and a region showing lyophobicity for it are formed on a substrate where the wiring is formed, and a droplet of the material for forming a wiring is added into the lyophilic region by an ink-jet method (for example, refer to Patent Document 3). An exposure device, a photomask, and the like are used for forming these lyophilic and lyophobic regions.
In addition, it is also disclosed that similarly in the wiring-forming technology by an ink-jet method, a bank is formed to surround a wiring-formed region and an upper part of this bank is provided with lyophobicity and the wiring-formed region is provided with lyophilicity, in order to suppress the material for the wiring from flowing out of the wiring-formed region (for example, refer to Patent Document 4). Also in preparation of this bank, a resist material having photosensitivity, an exposure device, a photomask, and the like, are used.
A technology of forming a TFT using only organic matters by an ink-jet method was also disclosed (for example, refer to Nonpatent Document 3).
If such an ink-jet method is used, a fluid material that is a material for a film to be formed is needed. However, a special production method is needed in order to obtain a film having characteristics equal to those of a film formed using a conventional vacuum deposition device, by a sputtering method or a CVD method. Therefore, such a method has not replaced the conventional method yet.
Further, it has been also proposed that using an ink-jet method, not the fluid material that is a material for a film to be formed but a resist material for forming a mask used when processing a thin film and the like on the substrate is added dropwise. This is a method of patterning a semiconductor layer of a TFT using a resist film which is formed by dropwise addition with an ink-jet method as a mask (for example, refer to Patent Document 5).
A TFT array substrate may be mentioned as a circuit substrate prepared through many photolithography processes, for example. The TFT array substrate includes a source wiring, a gate wiring, a TFT as a switching element connected to these wirings on a substrate, and is preferably used in a liquid crystal display device, and the like, for example. This TFT array substrate is produced through a series of steps shown in Nonpatent Document 4, and five or more photolithography processes are generally needed for production of the TFT array substrate.
[Patent Document 1]
Japanese Kokai Publication No. 2002-55363
[Patent Document 2]
WO 97/43689
[Patent Document 3]
Japanese Kokai Publication No. Hei-11-204529
[Patent Document 4]
Japanese Kokai Publication No. 2000-353594
[Patent Document 5]
Japanese Kokai Publication No. 2004-247704
[Nonpatent Document 1]
C. W. Kim, et al., “A Novel Four-Mask-Count Process Architecture for TFT-LCDs”, SID 00 DIGEST, (U.S.), Society for Information Display, 2000, vol. 31, first edition, p. 1006 to 1009.
[Nonpatent Document 2]
Nikkei electronics, issued on Jun. 17, 2002, Nikkei Business Publications, Jun. 17, 2002, No. 824, p. 67 to 78.
[Nonpatent Document 3]
Takeo Kawase, et al., “Invited Paper: All-Polymer Thin Film Transistors Fabricated by High-Resolution Ink-jet Printing”, SID 01 DIGEST, (U.S.), Society for Information Display, 2001, vol. 32, first edition, p. 40-43.
[Nonpatent Document 4]
Nikkei Micro Device edition, “Flat Panel Display 1999”, Nikkei Business Publications, 1998, p. 129.